Wireless communication systems are rapidly growing in usage. Further, wireless communication technology has evolved from voice-only communications to also include the transmission of data, such as Internet and multimedia content. A user equipment (“UE”) may be configured to establish a connection with different types of networks through the use of wireless communications protocols. Accordingly, based upon the capabilities of the hardware and software of the UE, the connection may be made with these different types of networks. For instance, the network may be a Universal Mobile Telecommunication System (“UMTS”) or Long Term Evolution (“LTE”) network for data connectivity, or the network may be a Global System for Mobile Communications (“GSM”) or Code Division Multiple Access (“CDMA”) network for voice connectivity.
LTE, commonly referred to a “4G LTE,” is a standard for wireless communication of high-speed data for mobile phones and data terminals. The LTE standard has been developed by the 3rd Generation Partnership Project (“3GPP”) and is described as a natural upgrade path for carriers using prior generation networks or “legacy” protocols or 2G/3G networks, such as GSM/UMTS protocols and CDMA 2000 1× (e.g., 1×RTT or simply “1×”) wireless communication protocols. Each of these different types of networks and protocols may be termed radio access technologies (“RATs”).
Through the usage of an all-Internet Protocol (“IP”) network, the LTE standard supports only packet switching (“PS”) data transmissions. Similar to many other protocols, an IP network breaks data into blocks and wraps the blocks into structures called packets. Each packet contains, along with the data load, information about the IP address of the source and the destination nodes, sequence numbers, control information, etc. In a circuit switched (“CS”) network, the communication channel remains open and in use throughout the duration of the call and the call data is transmitted all at once without being broken into blocks.
Since voice calls in GSM, UMTS and CDMA2000 utilize circuit switched data transmissions, carriers adopting the LTE standard need to re-engineer their voice call network. For instance, Voice over LTE (“VoLTE”) uses an IP multimedia subsystem (“IMS”) network having specific profiles for control and media planes of voice service on LTE. Accordingly, VoLTE communications result in the voice service being delivered as data flows within the LTE data bearer. Thus, there is no requirement for the legacy circuit-switched voice network to be maintained. Furthermore, VoLTE communications has up to three times more voice and data capacity than UMTS networks and up to six times more than GSM networks.
Furthermore, the 3GPP has standardized Single Radio Voice Call Continuity (“SRVCC”) to provide easy handovers from an LTE network to a GSM/UMTS network. Accordingly, SRVCC functionality is needed within VoLTE systems to enable a VoLTE call to be seamlessly handed over to legacy circuit switched voice systems, such as 2G/3G networks. However, SRVCC handover failures continue to be significant, especially in cell edge cases, where the coverage for LTE and legacy RATs is typically insufficient. Thus, the SRVCC handover failures not only result in call failures, but also decreased audio quality resulting in unsatisfactory user experience.